The present invention relates to an antilocking control system for the wheel brakes of vehicles of the type comprising sensors for monitoring the acceleration behavior of the vehicle wheels, an evaluation circuit which receives the signals from the sensors and which produces control signals from these signals, and a brake pressure control unit which receives the control signals from the evaluation circuit and which, in addition to a setting for pressure buildup, also has settings for brake pressure reduction and for at least approximately keeping the brake pressure constant. More particularly, the present invention relates to such an antilocking control system for the wheel brakes of a vehicle wherein the evaluation circuit includes a switching arrangement which produces a control signal for pressure reduction upon the occurrence of a tendency to lock, a control signal for keeping the pressure constant upon the subsequent occurrence of a wheel acceleration of a certain value, and normally also produces a control signal to keep the pressure constant in the transistion range between the end of the control signal for pressure reduction and the beginning of the control signal produced upon wheel acceleration (U.sub.+b).
Such an antilocking control system is known, for example, from German Pat. No. 1,655,380 which corresponds to U.S. Pat. No. 3,467,444, issued September 16th, 1969 to H. Leiber, the subject matter of which is incorporated herein. This patent, however, also provides a second lower deceleration threshold to effect a constant pressure which is of no significance to the present invention. In this known system, as soon as a higher deceleration threshold value has been exceeded, and until deceleration drops below that threshold value, the pressure is reduced; upon the occurrence of an acceleration signal the pressure is kept constant; and a memory member is provided which is charged when the outlet valve is enabled and discharged via the inlet valve at the end of the actuation of the outlet valve. Because of this discharge, the inlet valve remains excited, i.e., closed, at the end of the deceleration signal, i.e., there will be no immediate pressure buildup, rather the pressure is kept constant. The time constant of the delay member or memory is selected so that the interval between the end of the deceleration signal and the beginning of the acceleration signal is bridged, i.e., the pressure is kept constant during this time.